Bonding apparatus and bonding system

ABSTRACT

Deformation of substrates after the substrates are bonded can be suppressed. A bonding apparatus includes a first holding unit configured to attract and hold a first substrate from above; a second holding unit provided under the first holding unit and configured to attract and hold a second substrate from below; and a striker configured to press a central portion of the first substrate from above and bring the first substrate into contact with the second substrate. The first holding unit is configured to attract and hold a partial region of a peripheral portion of the first substrate, and the first holding unit attracts and holds the region which intersects with a direction, among directions from the central portion of the first substrate toward the peripheral portion thereof, in which a bonding region between the first substrate and the second substrate is expanded faster.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.15/670,072, filed on Aug. 7, 2017, which claims the benefit of JapanesePatent Application No. 2016-156083 filed on Aug. 9, 2016, the entiredisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The embodiments described herein pertain generally to a bondingapparatus and a bonding system.

BACKGROUND

Conventionally, there is known a bonding apparatus configured to bondsubstrates such as semiconductor wafers by an intermolecular force.

In this kind of bonding apparatus, by pushing down a central portion ofan upper substrate with a striker while holding an entire peripheralportion of the upper substrate, the central portion of the uppersubstrate is brought into contact with a central portion of a lowersubstrate. Accordingly, the central portions of the upper substrate andthe lower substrate are bonded by an intermolecular force, and a bondingregion is formed. Then, a so-called bonding wave is generated, wherebythe bonding region is expanded toward the peripheral portion of thesubstrate. Accordingly, the upper substrate and the lower substrate arebonded on their entire surfaces (See, for example, Patent Document 1).

To suppress a deformation of the substrates after they are bonded, it isdesirable that the bonding wave is expanded from the central portions ofthe substrates toward the peripheral portions thereof uniformly, thatis, in a concentric shape.

Patent Document 1: Japanese Patent Laid-open Publication No. 2015-095579

The bonding wave, however, is not actually expanded in the concentricshape but in a non-uniform manner. This is deemed to be because there isanisotropy in a physical property of a substrate, such as Young'smodulus or Poisson's ratio, and a velocity of the bonding wave in acertain crystal direction gets faster or slower than a velocity of thebonding wave in the other crystal direction by being affected by suchanisotropy.

Furthermore, it is also deemed to be because, though the bonding wave isexpanded in the concentric shape, a deformation amount of the substratecaused by a stress applied thereto is different depending on directionsdue to the anisotropy of Poisson's ratio or Young's modulus of thesubstrate.

SUMMARY

In view of the foregoing, exemplary embodiments provide a bondingapparatus and a bonding system capable of suppressing deformation ofsubstrates after the substrates are bonded.

In an exemplary embodiment, a bonding apparatus includes a first holdingunit, a second holding unit and a striker. The first holding unit isconfigured to attract and hold a first substrate from above. The secondholding unit is provided under the first holding unit and configured toattract and hold a second substrate from below. The striker isconfigured to press a central portion of the first substrate from aboveand bring the first substrate into contact with the second substrate.The first holding unit is configured to attract and hold a partialregion of a peripheral portion of the first substrate, and the firstholding unit attracts and holds the region which intersects with adirection, among directions from the central portion of the firstsubstrate toward the peripheral portion thereof, in which a bondingregion between the first substrate and the second substrate is expandedfaster.

According to the exemplary embodiment, it is possible to suppress thedeformation of the substrates after the substrates are bonded.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described asillustrations only since various changes and modifications will becomeapparent to those skilled in the art from the following detaileddescription. The use of the same reference numbers in different figuresindicates similar or identical items.

FIG. 1 is a schematic plan view illustrating a configuration of abonding system according to an exemplary embodiment;

FIG. 2 is a schematic side view illustrating the configuration of thebonding system according to the exemplary embodiment;

FIG. 3 is a schematic side view of a first substrate and a secondsubstrate;

FIG. 4 is a schematic plane view illustrating a configuration of abonding apparatus;

FIG. 5 is a schematic side view illustrating a configuration of thebonding apparatus;

FIG. 6 is a schematic side sectional view illustrating configurations ofan upper chuck and a lower chuck;

FIG. 7 is a diagram illustrating expansion of a bonding region in aconventional art;

FIG. 8 is a diagram illustrating expansion of the bonding region in theconventional art;

FIG. 9 is a schematic bottom view of the upper chuck;

FIG. 10 is a schematic perspective view of the lower chuck;

FIG. 11 is a schematic plan view of the lower chuck;

FIG. 12 is a schematic perspective sectional view illustrating aconfiguration of a protrusion part;

FIG. 13 is a flowchart illustrating a part of a processing performed bythe bonding system;

FIG. 14 is a diagram illustrating suction portions of the upper chuckfor use in a bonding processing according to the exemplary embodiment;

FIG. 15 is a diagram illustrating attraction regions of the lower chuckfor use in the bonding processing according to the exemplary embodiment;

FIG. 16 is a diagram for describing an operation of the bondingprocessing;

FIG. 17 is a diagram for describing an operation of the bondingprocessing;

FIG. 18 is a diagram for describing an operation of the bondingprocessing;

FIG. 19 is a diagram for describing an operation of the bondingprocessing;

FIG. 20 is a diagram for describing an operation of the bondingprocessing;

FIG. 21 is a schematic bottom view of an upper chuck according to amodification example; and

FIG. 22 is a schematic cross sectional view of a lower chuck accordingto the modification example.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the description. In thedrawings, similar symbols typically identify similar components, unlesscontext dictates otherwise. Furthermore, unless otherwise noted, thedescription of each successive drawing may reference features from oneor more of the previous drawings to provide clearer context and a moresubstantive explanation of the current exemplary embodiment. Still, theexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other embodiments may beutilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented herein. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein and illustrated in the drawings, may bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

Hereinafter, an exemplary embodiment of the present disclosure will beexplained in detail with reference to the accompanying drawings.

Hereinafter, a bonding apparatus and a bonding system according to thepresent disclosure will be explained in detail with reference to theaccompanying drawings. Further, it should be noted that the exemplaryembodiments are not intended to be anyway limiting.

1. Configuration of Bonding System

First, a configuration of a bonding system according to an exemplaryembodiment will be explained with reference to FIG. 1 to FIG. 3. FIG. 1is a schematic plan view illustrating a configuration of the bondingsystem according to the exemplary embodiment. FIG. 2 is a schematic sideview illustrating the configuration of the bonding system according tothe exemplary embodiment. FIG. 3 is a schematic side view illustrating afirst substrate and a second substrate.

In the following description, for the purposes of clear understanding,there may be used a rectangular coordinate system in which the X-axisdirection, Y-axis direction and Z-axis direction which are orthogonal toeach other are defined, and the positive Z-axis direction is regarded asa vertically upward direction. Furthermore, in the respective drawingsincluding FIG. 1 and FIG. 2, only the component parts relevant to theexplanation are illustrated, and illustration of general component partsmay be omitted.

A bonding system 1 according to the exemplary embodiment shown in FIG. 1is configured to form a combined substrate T by joining a firstsubstrate W1 and a second substrate W2 to each other (see FIG. 3).

The first substrate W1 is, for example, a semiconductor substrate suchas a silicon wafer or a compound semiconductor wafer on which a multiplenumber of electronic circuits are formed. The second substrate W2 is,for example, a bare wafer on which no electronic circuit is formed. Thefirst substrate W1 and the second substrate W2 have the substantiallysame diameter. Further, an electronic circuit may be formed on thesecond substrate W2.

In the description that follows, the first substrate W1 may sometimes bereferred to as “upper wafer W1”; the second substrate W2, “lower waferW2”; and the combined substrate T, “combined wafer T.” Further, in thefollowing description, as depicted in FIG. 3, among surfaces of theupper wafer W1, a surface to be bonded to the lower wafer W2 will bereferred to as “bonding surface W1 j,” and a surface opposite to thebonding surface W1 j will be referred to as “non-bonding surface W1 n.”Further, among surfaces of the lower wafer W2, a surface to be bonded tothe upper wafer W1 will be referred to as “bonding surface W2 j,” and asurface opposite to the bonding surface W2 j will be referred to as“non-bonding surface W2 n.”

As shown in FIG. 1, the bonding system 1 includes a carry-in/out station2 and a processing station 3. The carry-in/out station 2 and theprocessing station 3 are arranged in this sequence along the positiveX-axis direction. Further, the carry-in/out station 2 and the processingstation 3 are connected as a single body.

The carry-in/out station 2 includes a placing table 10 and a transfersection 20. The placing table 10 is equipped with a multiple number ofplacing plates 11. Provided on the placing plates 11 are cassettes C1,C2 and C3 each of which accommodates therein a plurality of (e.g., 25sheets of) substrates horizontally. For example, the cassette C1accommodates therein the upper wafers W1; the cassette C2, the lowerwafers W2; and the cassettes C3, the combined wafers T.

The transfer section 20 is provided adjacent to the positive X-axis sideof the placing table 10. Provided in the transfer section 20 are atransfer path 21 extended in the Y-axis direction and a transfer device22 configured to be movable along the transfer path 21. The transferdevice 22 is configured to be movable in the X-axis direction as well asin the Y-axis direction and pivotable around the Z-axis. Further, thetransfer device 22 is also configured to transfer the upper wafers W1,the lower wafers W2 and the combined wafers T between the cassettes C1to C3 placed on the placing plates 11 and a third processing block G3 ofthe processing station 3 to be described later.

Further, the number of the cassettes C1 to C3 placed on the placingplates 11 is not limited to the shown example. In addition, besides thecassettes C1 to C3, a cassette or the like for collecting a problematicsubstrate may be additionally provided on the placing plates 11.

A multiple number of, for example, three processing blocks G1, G2 and G3equipped with various kinds of devices are provided in the processingstation 3. For example, the first processing block G1 is provided at afront side (negative Y-axis side of FIG. 1) of the processing station 3,and the second processing block G2 is provided at a rear side (positiveY-axis side of FIG. 1) of the processing station 3. Further, the thirdprocessing block G3 is provided at a side of the carry-in/out station 2(negative X-axis side of FIG. 1) of the processing station 3.

Provided in the first processing block G1 is a surface modifyingapparatus 30 configured to modify the bonding surface W1 j of the upperwafer W1 and the bonding surface W2 j of the lower wafer W2. In thesurface modifying apparatus 30, the SiO₂ bond on the bonding surfaces W1j and W2 j of the upper wafer W1 and the lower wafer W2 is cut to beturned into SiO of a single bond, so that the bonding surfaces W1 j andW2 j are modified such that these surfaces are easily hydrophilizedafterwards.

Furthermore, in the surface modifying apparatus 30, for example, anoxygen gas or a nitrogen gas as a processing gas is excited into plasmaunder a decompressed atmosphere to be ionized. As these oxygen ions ornitrogen ions are irradiated to the bonding surfaces W1 j and W2 j ofthe upper wafer W1 and the lower wafer W2, the bonding surfaces W1 j andW2 j are plasma-processed to be modified.

In the second processing block G2, a surface hydrophilizing apparatus 40and a bonding apparatus 41 are disposed. The surface hydrophilizingapparatus 40 is configured to hydrophilize the bonding surfaces W1 j andW2 j of the upper wafer W1 and the lower wafer W2 with, for example,pure water, and then, clean the bonding surfaces W1 j and W2 j. In thesurface hydrophilizing apparatus 40, while rotating the upper wafer W1or the lower wafer W2 held by, for example, a spin chuck, the pure wateris supplied onto the upper wafer W1 or the lower wafer W2. Accordingly,the pure water supplied onto the upper wafer W1 or the lower wafer W2 isdiffused onto the bonding surfaces W1 j and W2 j of the upper wafer W1or the lower wafer W2, so that the bonding surfaces W1 j and W2 j arehydrophilized.

The bonding apparatus 41 is configured to bond the upper wafer W1 andthe lower wafer W2, which are hydrophilized, by an intermolecular force.A configuration of the bonding apparatus 41 will be discussed later.

In the third processing block G3, as shown in FIG. 2, transition (TRS)devices 50 and 51 for the upper wafer W1, the lower wafer W2 and thecombined wafer T are provided in two levels in this order from below.

Further, as illustrated in FIG. 1, a transfer section 60 is formed in aregion surrounded by the first processing block G1, the secondprocessing block G2 and the third processing block G3. A transfer device61 is provided in the transfer section 60. The transfer device 61 isequipped with, for example, a transfer arm which is configured to bemovable in a vertical direction and a horizontal direction and pivotablearound a vertical axis. The transfer device 61 is moved within thetransfer section 60 and transfers the upper wafers W1, the lower wafersW2 and the combined wafers T with respect to preset devices within thefirst processing block G1, the second processing block G2 and the thirdprocessing block G3 which are adjacent to the transfer section 60.

Furthermore, as depicted in FIG. 1, the bonding system 1 includes acontrol device 70. The control device 70 controls an operation of thebonding system 1. The control device 70 may be implemented by, forexample, a computer and includes a non-illustrated controller and anon-illustrated storage unit. The controller includes a microcomputerhaving a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM(Random Access Memory), an input/output port, or the like, or variouskinds of circuits. The CPU of the microcomputer implements a controloperation to be described later by reading and executing a programstored in the ROM. The storage unit may be implemented by, but notlimited to, a semiconductor memory device such a RAM or a flash memory,or a storage device such as a hard disc, an optical disc, or the like.

Further, the program may be recorded in a computer-readable recordingmedium and installed from the recording medium to the storage unit ofthe control device 70. The computer-readable recording medium may be, byway of non-limiting example, a hard disc (HD), a flexible disc (FD), acompact disc (CD), a magnet optical disc (MO), or a memory card.

2. Configuration of Bonding Apparatus

Now, a configuration of the bonding apparatus 41 will be explained withreference to FIG. 4 and FIG. 5. FIG. 4 is a schematic plan viewillustrating a configuration of the bonding apparatus 41. FIG. 5 is aschematic side view illustrating the configuration of the bondingapparatus 41.

As depicted in FIG. 4, the bonding apparatus 41 includes a processingvessel 100 having a hermetically sealable inside. A carry-in/out opening101 for the upper wafer W1, the lower wafer W2 and the combined wafer Tis formed on a lateral side of the processing vessel 100 at a side ofthe transfer region 60. A shutter 102 for opening/closing thecarry-in/out opening 101 is provided at the carry-in/out opening 101.

The inside of the processing vessel 100 is partitioned into a transferregion T1 and a processing region T2 by an inner wall 103. Theaforementioned carry-in/out opening 101 is formed on the lateral side ofthe processing vessel 100 in the transfer region T1. Further, the innerwall 103 is also provided with a carry-in/out opening 104 for the upperwafer W1, the lower wafer W2 and the combined wafer T.

A transition 110, a wafer transfer mechanism 111, an inverting mechanism130 and a position adjusting mechanism 120 are arranged in the transferregion T1 in this order from the carry-in/out opening 101, for example.

The transition 110 is configured to temporarily place thereon the upperwafer W1, the lower wafer W2 and the combined wafer T. The transition110 has two levels, for example, and is capable of holding any two ofthe upper wafer W1, the lower wafer W2 and the combined wafer T.

The wafer transfer mechanism 111 is equipped with a transfer armconfigured to be movable in the vertical direction (Z-axis direction)and the horizontal directions (Y-axis direction and X-axis direction)and also pivotable around a vertical axis, as shown in FIG. 4 and FIG.5. The wafer transfer mechanism 111 is capable of transferring the upperwafer W1, the lower wafer W2 and the combined wafer T within thetransfer region T1 or between the transfer region T1 and the processingregion T2.

The position adjusting mechanism 120 is configured to adjust a directionof the upper wafer T1 (lower wafer W2) in the horizontal direction. Toelaborate, the position adjusting mechanism 120 includes a base 121equipped with a non-illustrated holding unit configured to hold androtate the upper wafer W1 (lower wafer W2); and a detector 122configured to detect a position of a notch of the upper wafer W1 (lowerwafer W2). The position adjusting mechanism 120 adjusts the position ofthe notch of the upper wafer W1 (lower wafer W2) by detecting theposition of the notch with the detector 122 while rotating the upperwafer W1 (lower wafer W2) held by the base 121. Accordingly, theposition of the upper wafer W1 (lower wafer W2) in the horizontaldirection is adjusted.

The inverting mechanism 130 is configured to invert a front surface anda rear surface of the upper wafer W1. To elaborate, the invertingmechanism 130 is equipped with a holding arm 131 configured to hold theupper wafer W1. The holding arm 131 is extended in the horizontaldirection (X-axis direction). Further, the holding arm 131 is providedwith, for example, holding members 132 configured to hold the upperwafer W1 at four positions.

The holding arm 131 is supported by a driving unit 133 including, forexample, a motor or the like. The holding arm 131 is configured to berotatable around the horizontal axis by the driving unit 133. Further,the holding arm 131 is rotatable around the driving unit 133 and movablein the horizontal direction (X-axis direction). Another driving unit(not shown) including, for example, a motor or the like is providedunder the driving unit 133. The driving unit 133 can be moved in thevertical direction along a vertically extended supporting column 134 bythis another driving unit.

Further, the upper wafer W1 held by the holding members 132 can berotated around the horizontal axis through the driving unit 133 and canalso be moved in the vertical direction and the horizontal direction.Further, the upper wafer W1 held by the holding members 132 can be movedbetween the position adjusting mechanism 120 and an upper chuck 140 tobe described later by being rotated around the driving unit 133.

Provided in the processing region T2 are the upper chuck 140 configuredto hold and attract a top surface (non-bonding surface W1 n) of theupper wafer W1 from above; and a lower chuck 141 configured to place thelower wafer W2 thereon and hold and attract a bottom surface(non-bonding surface W2 n) of the lower wafer W2 from below. The lowerchuck 141 is disposed under the upper chuck 140 to face the upper chuck140.

As depicted in FIG. 5, the upper chuck 140 is held by an upper chuckholder 150 provided above the upper chuck 140. The upper chuck holder150 is provided at a ceiling surface of the processing vessel 100. Theupper chuck 140 is fixed to the processing vessel 100 with the upperchuck holder 150 therebetween.

The upper chuck holder 150 is equipped with an upper imaging unit 151configured to image the top surface (bonding surface W2 j) of the lowerwafer W2 held by the lower chuck 141. By way of non-limiting example,the upper imaging unit 151 is implemented by a CCD camera.

The lower chuck 141 is supported by a first lower chuck moving unit 160which is provided under the corresponding lower chuck 141. The firstlower chuck moving unit 160 is configured to move the lower chuck 141 inthe horizontal direction (X-axis direction), as will be described later.Further, the first lower chuck moving unit 160 is also configured tomove the lower chuck 141 in the vertical direction and rotate the lowerchuck 141 around the vertical axis.

The first lower chuck moving unit 160 is equipped with a lower imagingunit 161 configured to image the bottom surface (bonding surface W1 j)of the upper wafer W1 held by the upper chuck 140 (See FIG. 5). Thelower imaging unit 161 is implemented by, by way of example, a CCDcamera.

The first lower chuck moving unit 160 is mounted to a pair of rails 162which is provided at a bottom surface side of the first lower chuckmoving unit 160 and extended in the horizontal direction (X-axisdirection). The first lower chuck moving unit 160 is configured to bemoved along the rails 162.

The pair of rails 162 is provided on a second lower chuck moving unit163. The second lower chuck moving unit 163 is mounted on a pair ofrails 164 which is provided at a bottom surface side of the second lowerchuck moving unit 163 and extended in the horizontal direction (Y-axisdirection). This second lower chuck moving unit 163 is configured to bemoved in the horizontal direction (Y-axis direction) along the rails164. Further, the pair of rails 164 is provided on a placing table 165provided on the bottom surface of the processing vessel 100.

Now, configurations of the upper chuck 140 and the lower chuck 141 willbe explained with reference to FIG. 6. FIG. 6 is a schematic sidesectional view illustrating the configurations of the upper chuck 140and the lower chuck 141.

As illustrated in FIG. 6, the upper chuck 140 has a main body 170 havinga diameter equal to or larger than that of the upper wafer W1.

The main body 170 is supported by a supporting member 180 of the upperchuck holding unit 150. The supporting member 180 is configured to coverat least the main body 170 when viewed from the top and is fixed to themain body 170 by screwing, for example. The supporting member 180 issupported by a plurality of supporting columns 181 (see FIG. 5) providedat the ceiling surface of the processing vessel 100.

A through hole 176 is formed through central portions of the supportingmember 180 and the main body 170 in the vertical direction. A positionof the through hole 176 corresponds to the central portion of the upperwafer W1 attracted to and held by the upper chuck 140. A push pin 191 ofa striker 190 is inserted through the through hole 176.

The striker 190 is provided on a top surface of the supporting member180 and is equipped with the push pin 191, an actuator unit 192 and alinearly moving mechanism 193. The push pin 191 is a cylindrical memberextended along the vertical direction and is supported by the actuatorunit 192.

The actuator unit 192 is configured to generate a constant pressure in acertain direction (here, vertically downward direction) by air suppliedfrom, for example, an electro-pneumatic regulator (not shown). By theair supplied from the electro-pneumatic regulator, the actuator unit 192is capable of controlling a press load applied to the central portion ofthe upper wafer W1 as it is brought into contact with the centralportion of the upper wafer W1. Further, a leading end of the push pin191 is movable up and down in the vertical direction through the throughhole 176 by the air from the electro-pneumatic regulator.

The actuator unit 192 is supported at the linearly moving mechanism 193.The linearly moving mechanism 193 moves the actuator unit 192 in thevertical direction by a driving unit including a motor, for example.

The striker 190 is configured as described above, and controls amovement of the actuator unit 192 by the linearly moving mechanism 193and controls the press load upon the upper wafer W1 from the push pin191 by the actuator unit 192.

A plurality of pins 170 a is provided on a bottom surface of the mainbody 170, and these pins 170 a are in contact with the rear surface(non-bonding surface W1 n shown in FIG. 3) of the upper wafer W1.

At a part of the region where the pins 170 a are provided, the upperchuck 140 has an attraction region for attracting the upper wafer W1. Inthe present exemplary embodiment, this attraction region is provideddepending on anisotropy of a physical property of the upper wafer W1.

Here, the attraction region of the upper chuck 140 will be explainedwith reference to FIG. 7 to FIG. 9. FIG. 7 and FIG. 8 are diagramsillustrating expansion of a bonding region in a conventional art. FIG. 9is a schematic bottom view of the upper chuck 140.

As illustrated in FIG. 7, each of the upper wafer W1 and the lower waferW2 is a single crystal silicon wafer in which a crystal direction in adirection perpendicular to the surface (bonding surface) thereof is[100]. The notches N of the upper wafer W1 and the lower wafer W2 areformed at edges of the upper wafer W1 and the lower wafer W2 in acrystal direction of [011]. Further, each of the upper wafer W1 and thelower wafer W2 has a diameter of, for example, 300 mm.

If the central portion of the upper wafer W1 is pushed down and broughtinto contact with a central portion of the lower wafer W2, the centralportions of the upper wafer W1 and the lower wafer W2 are bonded by theintermolecular force, so that an bonding region A is formed at thecentral portions of both substrates. Then, a bonding wave is generated,whereby the bonding region A is expanded from the central portions ofthe substrates toward the peripheral portions thereof. As a result, theentire bonding surfaces W1 j and W2 j of the wafers W1 and W2 arebonded.

Here, the present inventors found out that the bonding region A is notexpanded in a concentric shape but in a non-uniform manner in case thatthe aforementioned bonding processing is performed while holding theupper wafer with the holding unit which holds the entire circumferenceof the peripheral portion of the upper wafer.

To elaborate, as depicted in FIG. 8, the bonding region A is expandedfaster toward directions at a cycle of 90° (directions of 45°, 135°,225° and 315° shown in FIG. 8, hereinafter referred to as “45°directions”) with respect to a direction oriented toward a [010] crystaldirection parallel to the surface of the upper wafer W1 from the centralportion of the upper wafer W1, as compared to directions at a cycle of90° (directions of 0°, 90°, 180° and 270° shown in FIG. 8, hereinafterreferred to as “90° directions”) with respect to a direction orientedtoward a [0-11] crystal direction parallel to the surface of the upperwafer W1 from the central portion of the upper wafer W1. As a result, asthe bonding region A which originally has a circular shape is expanded,the bonding region A becomes closer to a rectangular shape with the 45°directions as vertices.

The present inventors repeated researches and found out that thisnon-uniform expansion is caused by the anisotropy of the physicalproperty of the upper wafer W1 and the lower wafer W2 such as Young'smodulus.

By way of example, values of Young's modulus, Poisson's ratio and shearmodulus of the single crystal silicon wafer varies at a cycle of 90°. Toelaborate, the Young's modulus of the single crystal silicon wafer ishighest at a direction of 90° and is lowest at a direction of 45°.Further, the Poisson's ratio and the shear modulus are highest at thedirection of 45° and lowest at the direction of 90°.

As stated above, since the single crystal silicon wafer has theanisotropy in the physical property such as the Young's modulus, adistribution of a stress applied to the upper wafer W1 and a deformationthereof becomes non-uniform, not in the concentric shape. It is deemedthat this non-uniform distribution causes non-uniform expansion of thebonding region A, so that a deformation (distortion) of the combinedwafer T is deteriorated.

Thus, in the present exemplary embodiment, the entire circumference ofthe peripheral portion of the upper wafer W1 is not held, but onlyperipheral regions of the upper wafer W1 in the 45° directions where thebonding region A is expanded fastest are held by using the upper chuck140.

To be specific, as illustrated in FIG. 9, multiple suction portions 171to 175 configured to attract the upper wafer W1 by vacuum evacuation areprovided at the bottom surface of the main body 170 in the upper chuck140. Each of the suction portions 171 to 175 has the same height as thepins 170 a and comes into contact with the rear surface (non-bondingsurface W1 n) of the upper wafer W1.

First suction portions 171 and second suction portions 172 have circulararc-shaped attraction regions when viewed from the top, and arealternately arranged at a peripheral portion of the main body 170 alongthe circumference thereof at a regular distance.

A total number of four first suction portions 171 are arranged in the45° directions of the upper wafer W1, and a total number of four secondsuction portions 172 are arranged in the 90° directions of the upperwafer W1. To elaborate, centers of the circular arc-shaped attractionregions of the first suction portions 171 are located at positionscoincident with the 45° directions of the upper wafer W1, and centers ofthe circular arc-shaped attraction regions of the second suctionportions 172 are located at positions coincident with the 90° directionsof the upper wafer W1.

The four first suction portions 171 are connected to a single firstvacuum pump 171 b via first suction lines 171 a. Further, the fourthsecond suction portions 172 are connected to a single second vacuum pump172 b via second suction lines 172 a. The first suction portions 171 andthe second suction portions 172 attract the upper wafer W1 through thevacuum evacuation by the first vacuum pump 171 b and the second vacuumpump 172 b. Here, for the purpose of clear understanding, a lineconfiguration of only one of the multiple first suction portions 171 anda line configuration of only one of the multiple second suction portions172 are illustrated.

Third suction portions 173 and fourth suction portions 174 have circulararc-shaped attraction regions when viewed from the top, and arealternately arranged at an inner side of the main body 170 than thefirst suction portions 171 and the second suction portions 172 along thecircumference thereof at a regular distance.

Like the first suction portions 171, a total number of four thirdsuction portions 173 are arranged in the 45° directions of the upperwafer W1. To elaborate, centers of the circular arc-shaped attractionregions of the third suction portions 173 are located at positionscoincident with the 45° directions of the upper wafer W1. Further, eachthird suction portion 173 is positioned within a fan-shaped regionformed by two imaginary lines connecting a center of the main body 170and both ends of the first suction portion 171, and an edge of the firstsuction portion 171.

Like the second suction portions 172, a total number of four fourthsuction portions 174 are arranged in the 90° directions of the upperwafer W1. To elaborate, centers of the circular arc-shaped attractionregions of the fourth suction portions 174 are located at positionscoincident with the 90° directions of the upper wafer W1. Further, eachfourth suction portion 174 is positioned within a fan-shaped regionformed by two imaginary lines connecting the center of the main body 170and both ends of the second suction region 172, and an edge of thesecond suction portion 172.

Desirably, an angle range θ1 of the first suction portion 171 and thesecond suction portion 172, that is, an angle θ1 formed by the twoimaginary lines connecting the center of the main body 170 and the twoends of the first suction portion 171 (second suction portion 172) isequal to or higher than 38°. If θ1 is smaller than 38°, it may bedifficult to hold the upper wafer W1 appropriately. More desirably, θ1may be equal to or larger than 40° and equal to or smaller than 43°.That is to say, to reduce the non-uniformity of the bonding waveeffectively, it is desirable to set an angle range of a gap(non-attraction portion) formed between the first suction portion 171and the second suction portion 172 to be equal to or larger than 2° andequal to or smaller than 5°.

An angle range θ2 of the third suction portion 173 and the fourthsuction portion 174, that is, an angle θ2 formed by the two imaginarylines connecting the center of the main body 170 and the two ends of thethird suction portion 173 (fourth suction portion 174) is set to besmaller than the angle range θ1 of the first suction portion 171 (secondsuction portion 172). By way of non-limiting example, when θ1 is 43°, θ2is set to be 41°.

The four third suction portions 173 are connected to a single thirdvacuum pump 173 b via third suction lines 173 a. Further, the fourfourth suction portions 174 are connected to a single fourth vacuum pump174 b via fourth suction lines 174 a. The third suction portions 173 andthe fourth suction portions 174 attract the upper wafer W1 through thevacuum evacuation by the third vacuum pump 173 and the fourth vacuumpump 174. Here, for the purpose of clear understanding, the lineconfiguration of only one of the multiple third suction portions 173 anda line configuration of only one of the multiple fourth suction portions174 are illustrated.

A fifth suction portion 175 is provided at an inner side of the mainbody 170 than the third suction portions 173 and the fourth suctionportions 174. The fifth suction portion 175 has a circular ring-shapedattraction region when viewed from the top. The fifth suction portion175 is connected to a single fifth vacuum pump 175 b via a fifth suctionline 175 a. The fifth suction portion 175 attracts the upper wafer W1through the vacuum evacuation by the fifth vacuum pump 175 b.

As stated above, if a direction oriented toward the crystal direction of[0-11] parallel to the surface of the upper wafer W1 from the centralportion of the upper wafer W1 is defined as 0°, the multiple firstsuction portions 171 and the multiple third suction portions 173 arearranged at an interval of 90° with respect to the direction of 45°, andthe multiple second suction portions 172 and the multiple fourth suctionportions 174 are arranged at an interval of 90° with respect to thedirection of 0°. Further, the upper chuck 140 is capable of controllingan attraction force (including presence/absence of attraction) and anattraction timing for each of the first to fifth suction portions 171 to175.

Now, a configuration of the lower chuck 141 will be discussed withreference to FIG. 6 and FIG. 10 to FIG. 12. FIG. 10 is a schematicperspective view of the lower chuck 141. FIG. 11 is a schematic planview of the lower chuck 141, and FIG. 12 is a schematic perspectivesectional view illustrating a configuration of a protrusion part 260.

As depicted in FIG. 6, the lower chuck 141 includes a pad unit 200having a diameter equal to or larger than the lower wafer W2; and a basebody 250 provided under the pad unit 200. Multiple pins 200 a which comeinto contact with the rear surface (non-bonding surface W2 n) of thelower wafer W2 are provided on a top surface of the pad unit 200.

Further, a through hole 200 b is formed through a central portion of thepad unit 200 in the vertical direction. A position of the through hole200 b corresponds to the central portion of the lower wafer W2 attractedto and held by the lower chuck 141. Furthermore, the position of thethrough hole 200 b also corresponds to the position of the through hole176 formed in the upper chuck 140.

A main body 261 of the protrusion part 260 to be described later isinserted through the through hole 200 b. The main body 261 is protrudedfrom the through hole 200 b up to a position higher than the pins 200 aand supports the central portion of the lower wafer W2 at a higherposition than the rest portion of the lower wafer W2. The main body 261is provided at a position facing the push pin 191 of the striker 190.

As stated above, the upper wafer is brought into contact with the lowerwafer in the state that it is bent by the striker. As a result, a stressis applied to the upper wafer, and the combined wafer may be distorteddue to this stress.

Recently, there has been proposed a method of reducing a deformation ofthe combined wafer by forming an entire holding surface of the lowerchuck in a convex shape and maintaining the lower wafer thereon in abent state. In this conventional method, however, it has been difficultto cope with a local deformation of the central portion of the combinedwafer caused by the striker.

From this consideration, in the bonding apparatus 41 according to thepresent exemplary embodiment, the protruding part is provided at theposition of the lower chuck 141 facing the striker 190. With thisconfiguration, the two wafers W1 and W2 can be joined in the state thatthe same stress as the local stress applied to the central portion ofthe upper wafer W1 by the striker 190 is applied to the lower wafer W2.Thus, the local deformation caused by the striker 190 can be reduced.

A top surface of the main body 261 of the protrusion part 260 has adiameter equal to a diameter of a bottom surface of the push pin 191 ofthe striker 190. Accordingly, a stress closer to the local stressapplied to the upper wafer W1 by the push pin 191 can be applied to thelower wafer W2.

As shown in FIG. 10, the pad unit 200 has a first rib 201 and a secondrib 202. The first rib 201 and the second rib 202 are arranged in aconcentric shape in the order of the first rib 201 and the second rib202 from an inner side with respect to a center of the pad unit 200. Thefirst rib 201 and the second rib 202 have the same height as the pins200 a. The second rib 202 is provided at a peripheral portion of the padunit 200 and supports a peripheral portion of the lower wafer W2.

With the first rib 201 and the second rib 202, the top surface of thepad unit 200 is partitioned into an inner attraction region 210 forattracting a region including the central portion of the lower wafer W2;and an outer attraction region 220 for attracting a region including theperipheral portion of the lower wafer W2.

The outer attraction region 220 has a planar shape. In other words, theouter attraction region 220 attracts the lower wafer W2 by the multiplepins 200 a in a planar manner. Meanwhile, the portion of the innerattraction region 210 facing the striker 190 is protruded due to thepresence of the protrusion part 260, as mentioned above. The restportion of the inner attraction region 210 other than the protrusionpart 260 is of a planar shape.

Further, the pad unit 200 is equipped with a multiple number of thirdribs 203 extended in a radial shape from the first rib 201 toward thesecond rib 202. The outer attraction region 220 is partitioned by thesethird ribs 203 into multiple division regions 230 and 240 which arearranged alternately along the circumferential direction thereof.

Among the multiple division regions 230 and 240, the first divisionregions 230 are placed in a first direction, among directions from thecentral portion of the lower wafer W2 toward the peripheral portionthereof, where the bonding region A (see FIG. 7) between the upper waferW1 and the lower wafer W2 is expanded fastest. Further, among themultiple division regions 230 and 240, the second division regions 240are arranged next to the first division regions 230 in thecircumferential direction and are placed in a second direction, amongthe directions from the central portion of the lower wafer W2 toward theperipheral portion thereof, where the bonding region A is expandedslowly as compared to that in the first direction.

To elaborate, if a direction oriented toward the crystal direction of[0-11] parallel to the surface of the lower wafer W2 from the centralportion of the lower wafer W2 is defined as 0°, the multiple firstdivision regions 230 are arranged at an interval of 90° with respect tothe direction of 45°, and the multiple second division regions 240 arearranged at an interval of 90° with respect to the direction of 0°. Thatis, the multiple first division regions 230 are arranged in the 45°directions, like the first suction portions 171 of the upper chuck 140,whereas the multiple second division regions 240 are arranged in the 90°directions, like the second suction portions 172 of the upper chuck 140.

Further, the pad unit 200 further includes a fourth rib 204. The forthrib 204 is provided between the first rib 201 and the second rib 202 ina concentric shape with respect to the first rib 201 and the second rib202. With this fourth rib 204, each of the first division regions 230 ispartitioned into a first outer division region 231 and a first innerdivision region 232, and each of the second division regions 240 ispartitioned into a second outer division region 241 and a second innerdivision region 242. The first outer division region 231 and the firstinner division region 232 have the same attraction area. Likewise, thesecond outer division region 241 and the second inner division region242 have the same attraction area.

As depicted in FIG. 11, multiple first suction openings 210 a are formedin a region of the pad unit 200 corresponding to the inner attractionregion 210. These multiple first suction openings 210 a are arrangedcircumferentially to surround the protrusion part 260. Further, asuction space 250 a communicating with the multiple first suctionopenings 210 a is formed in the base body 250, and the suction space 250a is connected to a first vacuum pump 211 b via a first suction line 211a. With this configuration, by arranging the multiple first suctionopenings 210 a around the protrusion part 260, the central portion ofthe lower wafer W2 can be attracted uniformly along the circumferentialdirection thereof.

Furthermore, a second suction opening 230 a, a third suction opening 230b, a fourth suction opening 240 a and a fifth suction opening 240 b areformed in regions of the pad unit 200 corresponding to each first outerdivision region 231, each first inner division region 232, each secondouter division region 241 and each second inner division region 242,respectively. By way of example, the second suction opening 230 a, thethird suction opening 230 b, the fourth suction opening 240 a and thefifth suction opening 240 b are formed in central portions of the firstouter division region 231, the first inner division region 232, thesecond outer division region 241 and the second inner division region242, respectively.

The second suction openings 230 a, the third suction openings 230 b, thefourth suction openings 240 a and the fifth suction openings 240 b areconnected to a second vacuum pump 231 b, a third vacuum pump 232 b, afourth vacuum pump 241 b and a fifth vacuum pump 242 b via secondsuction lines 231 a, third suction lines 232 a, fourth suction lines 241a and fifth suction lines 242 a, respectively.

With this configuration, the lower chuck 141 is capable of controllingthe attraction force (including the presence/absence of attraction) andthe attraction timing for each of the inner attraction region 210, thefirst outer division regions 231, the first inner division regions 232,the second outer division regions 241 and the second inner divisionregions 242.

Further, in FIG. 11, for the purpose of clear understanding, the lineconfiguration of only one of the multiple first outer division regions231, the line configuration of only one of the multiple first innerdivision regions 232, the line configuration of only one of the multiplesecond outer division regions 241 and the line configuration of only oneof the multiple second inner division regions 242 are illustrated.

As depicted in FIG. 12, the protrusion part 260 is provided to beattachable and detachable with respect to the inner attraction region210. To elaborate, the protrusion part 260 includes a verticallyextended cylindrical main body 261; and a flange portion 262 which isprovided at a base end of the main body 261 and has a larger diameterthan the main body 261. Further, formed in the inner attraction region210 of the pad unit 200 are a through hole 200 b and a recess 200 cwhich communicates with the through hole 200 b and is provided on abottom surface of the inner attraction region 210. The main body 261 ofthe protrusion part 260 is inserted through the through hole 200 b fromthe bottom surface side of the inner attraction region 210 and thenprotruded to a top surface of the inner attraction region 210. Theflange portion 262 of the protrusion part 260 is fitted into the recess200 c of the inner attraction region 210 to be in contact with therecess 200 c. The protrusion part 260 is fixed to the inner attractionregion 210 by a fixing member 263 such as a screw.

In addition, a shim member 265 configured to adjust a protruding amountof the main body 261 from the inner attraction region 210 is providedbetween the recess 200 c of the inner attraction region 210 and theflange portion 262 of the protrusion part 260.

As stated above, by configuring the protrusion part 260 to be attachableto and detachable from the inner attraction region 210 and allowing theprotruding amount of the main body 261 to be adjusted by the shim member265, it may be possible to change a push-up amount of the lower wafer W2by the protrusion part 260 easily depending on a variation of apush-down amount of the upper wafer W1 by the striker 190, for example.

3. Specific Operation of Bonding System

Now, a specific operation of the bonding system 1 will be explained withreference to FIG. 13 to FIG. 20. FIG. 13 is a flowchart for describing apart of a processing performed by the bonding system 1. FIG. 14 is adiagram illustrating the suction portions of the upper chuck 140 for usein the bonding processing according to the present exemplary embodiment.FIG. 15 is a diagram illustrating the attraction regions of the lowerchuck 141 for use in the bonding processing according to the presentexemplary embodiment. FIG. 16 to FIG. 20 are diagrams for describingoperations of the bonding processing. Further, various processings shownin FIG. 13 are performed under the control of the control device 70.

First, a cassette C1 accommodating a plurality of upper wafers W1, acassette C2 accommodating a plurality of lower wafers W2 and an emptycassette C3 are placed on the preset placing plates 11 of thecarry-in/out station 2. Then, an upper wafer W1 is taken out of thecassette C1 by the transfer device 22 and is transferred to thetransition device 50 of the third processing block G3 of the processingstation 3.

Subsequently, the upper wafer W1 is transferred into the surfacemodifying apparatus 30 of the first processing block G1 by the transferdevice 61. In the surface modifying apparatus 30, an oxygen gas as theprocessing gas is excited into plasma and ionized under the presetdecompressed atmosphere. The oxygen ions are irradiated to the bondingsurface W1 j of the upper wafer W1, and the bonding surface W1 j isplasma-processed. As a result, the bonding surface W1 j of the upperwafer W1 is modified (process S101).

Then, the upper wafer W1 is transferred into the surface hydrophilizingapparatus 40 of the second processing block G2 by the transfer device61. In the surface hydrophilizing apparatus 40, the pure water issupplied onto the upper wafer W1 while rotating the upper wafer W1 heldby the spin chuck. The supplied pure water is diffused on the bondingsurface W1 j of the upper wafer W1, and hydroxyl groups (silanol groups)adhere to the bonding surface W1 j of the upper wafer W1 modified in thesurface modifying apparatus 30, so that the bonding surface W1 j ishydrophilized. Further, the bonding surface W1 j of the upper wafer W1is cleaned by the corresponding pure water (process S102).

Thereafter, the upper wafer W1 is transferred into the bonding apparatus41 of the second processing block G2 by the transfer device 61. Theupper wafer W1 carried into the bonding apparatus 41 is then transferredinto the position adjusting mechanism 120 through the transition 110 bythe wafer transfer mechanism 111. Then, the direction of the upper waferW1 in the horizontal direction is adjusted by the position adjustingmechanism 120 (process S103).

Afterwards, the upper wafer W1 is delivered onto the holding arm 131 ofthe inverting mechanism 130 from the position adjusting mechanism 120.Then, in the transfer region T1, by inverting the holding arm 131, thefront surface and the rear surface of the upper wafer W1 are inverted(process S104). That is, the bonding surface W1 j of the upper wafer W1is turned to face down.

Thereafter, the holding arm 131 of the inverting mechanism 130 is movedto be located under the upper chuck 140 by being rotated. The upperwafer W1 is then transferred to the upper chuck 140 from the invertingmechanism 130. Specifically, the non-bonding surface W1 n of the upperwafer W1 is attracted to and held by the upper chuck 140 in the statethat the notch N of the upper wafer W1 is oriented to a predetermineddirection, that is, in a direction where the second suction portion 172and the fourth suction portion 174 are provided (process S105).

In the process S105, the upper chuck 140 attracts and holds the upperwafer W1 by using, among the first to fifth suction portions 171 to 175,the first suction portions 171 and the third suction portions 173arranged at the 45° directions as well as the fifth suction portion 175(see FIG. 14).

While the above-described processes S101 to S105 are being performed onthe upper wafer W1, a processing of the lower wafer W2 is performed.First, the lower wafer W1 is taken out of the cassette C2 by thetransfer device 22 and transferred into the transition device 50 of theprocessing station 3 by the transfer device 22.

Thereafter, the lower wafer W2 is transferred into the surface modifyingapparatus 30 by the transfer device 61, and the bonding surface W2 j ofthe lower wafer W2 is modified (process S106). Further, the modificationof the bonding surface W2 j of the lower wafer W2 in the process S106 isthe same as the above-stated process S101.

Subsequently, the lower wafer W2 is transferred into the surfacehydrophilizing apparatus 40 by the transfer device 61, so that thebonding surface W2 j of the lower wafer W2 is hydrophilized and cleaned(process S107). The hydrophilizing and the cleaning of the bondingsurface W2 j of the lower wafer W2 in the process S107 are the same asthose in the above-described process S102.

Then, the lower wafer W2 is transferred into the bonding apparatus 41 bythe transfer device 61. The lower wafer W2 carried into the bondingapparatus 41 is transferred into the position adjusting mechanism 120through the transition 110 by the wafer transfer mechanism 111. Then,the direction of the lower wafer W2 in the horizontal direction isadjusted by the position adjusting mechanism 120 (process S108).

Afterwards, the lower wafer W2 is transferred onto the lower chuck 141by the wafer transfer mechanism 111 and attracted to and held by thelower chuck 141 (process S109). Here, the non-bonding surface W2 n ofthe lower wafer W2 is attracted to and held by the lower chuck 141 inthe state that the notch N of the lower wafer W2 is oriented to apredetermined direction which is the same as the direction of the notchN of the upper wafer W1, that is, in a direction where the first outerdivision region 231 and the first inner division region 232 areprovided.

In the process S109, the lower chuck 141 attracts and holds the lowerwafer W2 by using, among the inner attraction region 210, the firstouter division regions 231, the first inner division regions 232, thesecond outer division regions 241 and the second inner division regions242, the first outer division regions 231 and the first inner divisionregions 232 arranged at the 45° direction as well as the innerattraction region 210 (see FIG. 15).

Subsequently, the horizontal positions of the upper wafer W1 held by theupper chuck 140 and the lower wafer W2 held by the lower chuck 141 areadjusted (process S110).

Then, the vertical positions of the upper wafer W1 held by the upperchuck 140 and the lower wafer W2 held by the lower chuck 141 areadjusted (process S111). To elaborate, as the first lower chuck movingunit 160 moves the lower chuck 141 in the vertical direction, the lowerwafer W2 approaches the upper wafer W1. Accordingly, a distance betweenthe bonding surface W2 j of the lower wafer W2 and the bonding surfaceW1 j of the upper wafer W1 is adjusted to a preset distance, forexample, 50 μm to 200 μm (see FIG. 16).

Afterwards, as shown in FIG. 17, after releasing the attraction and theholding of the upper wafer W1 by the fifth suction portion 175 (processS112), as shown in FIG. 18, by lowering the push pin 191 of the striker190, the central portion of the upper wafer W1 is pushed down (processS113). By maintaining the attraction and the holding of the centralportion of the upper wafer W1 by using the fifth suction portion 175until a time immediately before the upper wafer W1 is pushed down by thestriker 190, a bending (for example, about 1 μm) of the central portionof the upper wafer W1 can be suppressed. Accordingly, in case of settingthe distance between the upper wafer W1 and the lower wafer W2 to anarrow gap smaller than, e.g., 30 μm in the process S112, an increase ofdifficulty in adjusting parallelism between the upper chuck 140 and thelower chuck 141 can be suppressed.

If the central portion of the upper wafer W1 is brought into contactwith a central portion of the lower wafer W2 and the central portion ofthe upper wafer W1 and the central portion of the lower wafer W2 arepressed at a preset force as the upper wafer W1 is pushed down by thestriker 190, the bonding is started between the central portion of theupper wafer W1 and the central portion of the lower wafer W2 which arepressed against each other. That is, since the bonding surface W1 j ofthe upper wafer W1 and the bonding surface W2 j of the lower wafer W2have been modified in the processes S101 and S106, respectively, Van derWaals force (intermolecular force) is generated between the bondingsurfaces W1 j and W2 j, so that the bonding surfaces W1 j and W2 j arebonded. Further, since the bonding surface W1 j of the upper wafer W1and the bonding surface W2 j of the lower wafer W2 have beenhydrophilized in the processes S102 and S107, respectively, hydrophilicgroups between the bonding surfaces W1 j and W2 j are hydrogen-bonded,so that the bonding surfaces W1 j and W2 j are firmly bonded. As aresult, the bonding region A (see FIG. 7) is formed.

In the bonding apparatus 41 according to the present exemplaryembodiment, the protrusion part 260 is provided at the position of thelower chuck 141 facing the striker 190. Accordingly, in the state thatthe same stress as the local stress applied to the central portion ofthe upper wafer W1 by the striker 190 is applied to the lower wafer W2,the two wafers W1 and W2 are joined. Therefore, the local deformation ofthe combined wafer T that might be caused by the striker 190 can bereduced.

Thereafter, the bonding wave which is expanded from the central portionsof the upper wafer W1 and the lower wafer W2 toward the peripheralportions thereof takes place between the upper wafer W1 and the lowerwafer W2.

In the bonding apparatus 41 according to the present exemplaryembodiment, the first to fourth suction portions 171 to 174 are arrangedaccording to the anisotropy of the upper wafer W1, and the upper waferW1 is attracted and held by using the first suction portions 171 and thethird suction portions 173 arranged at the 45° directions in which thebonding region A is expanded fastest. That is to say, the upper wafer W1is not attracted and held in the 90° directions in which the bondingregion A is expanded most slowly.

Accordingly, as compared to the case where the entire circumference ofthe peripheral portion of the upper wafer W1 is attracted and held, thenon-uniform distribution of the stress applied to the upper wafer W1 andthe deformation thereof can be suppressed. As a result, thenon-uniformity of the bonding wave is reduced, and the bonding region Acan be expanded in a nearly concentric shape. As a result, in thebonding apparatus 41 according to the present exemplary embodiment, thedeformation (distortion) of the combined wafer T can be reduced.

Furthermore, the present inventors also analyzed the stress distributionand the displacement amount of the combined wafer for each of cases ofholding the entire circumference of the peripheral portion of the upperwafer, holding the upper wafer only in the 45° directions and holdingthe upper wafer only in the 90° directions, and it is confirmed that thestress distribution and the displacement amount of the combined waferare most uniform in the case of holding the upper wafer only in the 45°directions.

Further, in the present exemplary embodiment, the lower chuck 141 isalso designed to hold the lower wafer W2 only in the 45° directions, notthe entire surface thereof, in the same manner as the upper chuck 140holds the upper wafer W1. That is, among the first outer divisionregions 231, the first inner division regions 232, the second outerdivision regions 241 and the second inner division regions 242, thelower wafer W2 is attracted and held by using the first outer divisionregions 231 and the first inner division regions 232 arranged in the 45°directions.

Accordingly, since the stress states of the upper wafer W1 and the lowerwafer W2 can be made same, the deformation (distortion) of the combinedwafer T can be further reduced. However, the lower chuck 141 is notlimited to holding the lower wafer W2 only in the 45° directions but maybe configured to hold the entire surface of the lower wafer W2.

Thereafter, as shown in FIG. 19, while pressing the central portion ofthe upper wafer W1 against the central portion of the lower wafer W2 bythe push pin 191, the attraction and the holding of the upper wafer W1by the third suction portions 173 is released (process S114).Thereafter, the attraction and the holding of the upper wafer W1 by thefirst suction portions 171 is released (process S115). As a result, asillustrated in FIG. 20, the upper wafer W1 and the lower wafer W2 arebonded to each other on the entire bonding surfaces W1 j and W2 jthereof.

Afterwards, the push pin 191 is raised up to the upper chuck 140, andthe attraction and the holding of the lower wafer W2 by the lower chuck141 is released. Then, the combined wafer T is transferred to thetransition device 51 by the transfer device 61, and then, is transferredinto the cassette C3 by the transfer device 22 of the carry-in/outstation 2. Through these processes, the series of bonding processing arecompleted.

As stated above, the bonding apparatus 41 according to the presentexemplary embodiment includes the upper chuck 140 (an example of a firstholding unit), the lower chuck 141 (an example of a second holding unit)and the striker 190. The upper chuck 140 attracts and holds the upperwafer W1 (an example of the first substrate) from above. The lower chuck141 is disposed under the upper chuck 140, and is configured to attractand hold the lower wafer W2 (an example of the second substrate) frombelow it. The striker 190 presses the central portion of the upper waferW1 from above and brings the central portion of the upper wafer W1 intocontact with the lower wafer W2. Further, the upper chuck 140 attractsand holds a part of the peripheral portion of the upper wafer W1.Specifically, among the directions from the central portion of the upperwafer W1 toward the peripheral portion thereof, the upper chuck 140attracts and holds the regions of the upper wafer W1 intersecting withthe direction in which the bonding region A between the upper wafer W1and the lower wafer W2 is expanded fastest.

Accordingly, the non-uniformity of the bonding wave is reduced, and thebonding region A is expanded in a nearly concentric shape. Therefore,the deformation of the combined wafer T can be reduced.

Furthermore, the bonding apparatus 41 according to the present exemplaryembodiment includes the upper chuck 140 (the example of the firstholding unit), the lower chuck 141 (the example of the second holdingunit) and the striker 190. The upper chuck 140 is configured to hold theupper wafer W1 (the example of the first substrate) from above. Thelower chuck 141 (the example of the second holding unit) is disposedunder the upper chuck 140, and is configured to attract and hold thelower wafer W2 from below. The striker 190 presses the central portionof the upper wafer W1 and brings it into contact with the lower waferW2. Further, the lower chuck 141 includes the inner attraction region210 configured to attract the region of the lower wafer W2 including thecentral portion thereof; and the outer attraction region 220 which isprovided outside the inner attraction region 210 to be arrangedconcentrically with the inner attraction region 210 and is configured toattract the region of the lower wafer W2 including the peripheralportion thereof. Further, the inner attraction region 210 has the shapein which at least a part of the inner attraction region 210 facing thestriker 190 is protruded, and the outer attraction region 220 has theplanar shape.

Thus, according to the bonding apparatus 41 of the present exemplaryembodiment, the local deformation caused by the striker 190 can bereduced.

4. Modification Example

Now, a modification example of the above-described exemplary embodimentwill be explained. FIG. 21 is a schematic bottom view of an upper chuckaccording to the modification example. FIG. 22 is a schematic crosssectional view of a lower chuck according to the modification example.In the following description, parts identical to those already describedabove will be assigned same reference numerals, and redundantdescription will be omitted.

In the above-described exemplary embodiment, in the bonding processing,the upper wafer W1 in the 45° directions are attracted and held by usingonly the first suction portions 171 and the third suction portions 173of the upper chuck 140. That is to say, the second suction portions 172and the fourth suction portions 174 configured to attract and hold theupper wafer W1 in the 90° directions are not used. If, however, there isa holding method in which the stress applied to the regions of the upperwafer W1 in the 90° directions becomes relatively smaller than thestress applied to the regions of the upper wafer W1 in the 45°directions, it may be possible to attract and hold the upper wafer W1both in the 45° directions and the 90° directions.

In such a case, for example, the regions of the upper wafer W1 in the90° directions may be attracted and held with a force smaller than aforce for the regions of the upper wafer W1 in the 45° directions. Thatis, the upper chuck 140 may hold the regions of the upper wafer W1 inthe 45° directions with a first attraction force by using the firstsuction portions 171 and the third suction portions 173 while holdingthe regions of the upper wafer W1 in the 90° directions with a secondattraction force smaller than the first attraction force by using thesecond suction portions 172 and the fourth suction portions 174. Controlof the attraction forces may be achieved by providing a pressurecontroller at a front end of each vacuum pump and controlling thesepressure controllers under the control of the control device 70.

Further, after the upper chuck 140 pushes down the central portion ofthe upper wafer W1 by using the striker 190 while attracting and holdingthe upper wafer W1 by using the first to fourth suction portions 171 to174, the attraction by the fourth suction portions 174 may be releasedat a timing earlier than a timing when the attraction by the thirdsuction portions 173 is released. Further, the upper chuck 140 mayrelease the attraction by the second suction portions 172 at a timingearlier than a timing when the attraction by the first suction portions171 is released.

As stated above, by providing the first suction portions 171 and thethird suction portions 173 corresponding to the 45° directions of theupper wafer W1 and the second suction portions 172 and the fourthsuction portions 174 corresponding to the 90° directions of the upperwafer W1 and controlling these suction portions 171 to 174 individually,the velocities of the bonding wave in the 45° directions and the 90°directions can be adjusted more precisely. Accordingly, as compared tothe case of using only the first suction portions 171 and the thirdsuction portions 173 corresponding to the 45° directions, thedeformation of the combined wafer T can be further reduced.

Moreover, in the above-described exemplary embodiment, though the thirdsuction portions 173 and the fourth suction portions 174 are configuredto be controllable individually, the third suction portions 173 and thefourth suction portions 174 need not necessarily be controllableindividually. That is, the third suction portions 173 and the fourthsuction portions 174 may be connected to a single vacuum pump.

In addition, in the above-described exemplary embodiment, the upperchuck 140 includes the first to fifth suction portions 171 to 175.However, the upper chuck 140 needs to be equipped with at least thefirst suction portions 171, and may not necessarily have the othersuction portions 172 to 175.

By way of example, as shown in FIG. 21, an upper chuck 140A may be onlyequipped with the first suction portions 171 and the third suctionportions 173. That is, it may include neither of the second suctionportions 172, the fourth suction portions 174 and the fifth suctionportion 175. Further, an upper chuck may be only equipped with the firstsuction portions 171, the second suction portions 172 and the fifthsuction portion 175. Still further, an upper chuck may be only equippedwith the first suction portions 171 and the second suction portions 172,or the first suction portions 171 and the fifth suction portion 175.

Moreover, though the above exemplary embodiment has been described forthe case where the upper wafer W1 and the lower wafer W2 are singlecrystal silicon wafers, the kind of the substrates may not be limited tothe single crystal silicon wafer. That is, the arrangement of theattraction regions of the upper chuck and the lower chuck may not belimited to the 45° directions and the 90° directions, but the attractionregions may be arranged according to the anisotropy of the physicalproperty of the substrates held by the upper chuck and the lower chuck.

Further, though the above exemplary embodiment has been described forthe case where the lower chuck 141 is equipped with the detachableprotrusion part 260, the protrusion part 260 may not necessarily bedetachable. For example, the protrusion part 260 may be implemented by aprotrusion formed as one body with the pad unit 200.

Further, the inner attraction region 210 may be configured to bedeformed between in a flat state without being protruded upwards and ina convex state where the inner attraction region 210 is protrudedupwards with respect to the central portion thereof as a peak.

By way of example, as illustrated in FIG. 22, a lower chuck 141Aincludes an inner attraction region 210A and an outer attraction region220A. The inner attraction region 210A includes a deformable stage 211and a fixing ring 212. The deformable stage 211 has a substantiallycircular shape when viewed from the top, and a front surface side of thedeformable stage 211, which holds the lower wafer W2 thereon, is of aplanar shape in a non-deformation state where it is not deformed.

A peripheral portion of the deformable stage 211 is fixed to a base body250A by the fixing ring 212 having a substantially annular shape. Thebase body 250A is fixed to the first lower chuck moving unit 160 (seeFIG. 4).

The deformable stage 211 is configured to be convexly deformed. Here,the term “convex deformation” refers to a deformation in which a centralportion of the deformable stage 211 is displaced to a higher positionthan a peripheral portion thereof and includes a case where thedeformable stage 211 is upwardly curved toward the peripheral portionfrom the central portion thereof and becomes a part of a substantiallyspherical surface shape, as shown in FIG. 22.

A structure in which the deformable stage 211 is convexly deformed isnot particularly limited. By way of non-limiting example, an airpressure may be used or a piezo actuator or the like may be used.

As an example, in case of using the piezo actuator, multiple piezoactuators are provided within the base body 250A. One of the multiplepiezo actuators may be provided at a position corresponding to thecentral portion of the deformable stage 211, and the others may beequi-spaced on a single circle around the peripheral portion of thedeformable stage 211.

Each piezo actuator is disposed with a top piece as a driving unitfacing vertically upwards. Further, each piezo actuator has piezoelements stacked therein and moves each top piece up and down dependingon a variation in voltages from non-illustrated voltage generatorsconnected to each of the piezo elements. The deformable stage 211 isdeformed according to a movement of each top piece.

As stated above, by using the piezo actuator, a deformation structure ofthe deformable stage 211 can be configured. Further, the type of theactuator is not merely limited to the piezo actuator as long as theactuator is capable converting an input energy to a physical motion in avertical direction.

Further, in the above-described exemplary embodiment, the first divisionregion 230 of the lower chuck 141 is divided into the first outerdivision region 231 and the first inner division region 232, and thesecond division region 240 of the lower chuck 141 is divided into thesecond outer division region 241 and the second inner division region242. However, the first division region 230 and the second divisionregion 240 need not be necessarily divided. Furthermore, though theouter attraction region 220 is divided into the first division region230 and the second division region 240 in the above-described exemplaryembodiment, the outer attraction region 220 need not necessarily bedivided.

From the foregoing, it will be appreciated that the exemplary embodimentof the present disclosure has been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the embodiment disclosed herein is not intended to belimiting. The scope of the inventive concept is defined by the followingclaims and their equivalents rather than by the detailed description ofthe exemplary embodiment. It shall be understood that all modificationsand embodiments conceived from the meaning and scope of the claims andtheir equivalents are included in the scope of the inventive concept.

The claims of the present application are different and possibly, atleast in some aspects, broader in scope than the claims pursued in theparent application. To the extent any prior amendments orcharacterizations of the scope of any claim or cited document madeduring prosecution of the parent could be construed as a disclaimer ofany subject matter supported by the present disclosure, Applicantshereby rescind and retract such disclaimer. Accordingly, the referencespreviously presented in the parent applications may need to berevisited.

We claim:
 1. A bonding apparatus, comprising: a first holding unitconfigured to attract and hold a first substrate from above; a secondholding unit provided under the first holding unit and configured toattract and hold a second substrate from below; and a striker configuredto press a central portion of the first substrate from above and bringthe first substrate into contact with the second substrate, wherein thefirst holding unit is configured to attract and hold a partial region ofa peripheral portion of the first substrate, when a bonding regionbetween the first substrate and the second substrate has vertices of ashape closer to a polygonal shape that is expanded from a circularshape, the partial region includes a region intersecting with at leastone direction from the central portion of the first substrate toward thevertices.
 2. The bonding apparatus of claim 1, wherein the directionfrom the central portion toward the vertices is a direction in which thebonding region between the first substrate and the second substrate isexpanded fastest.
 3. The bonding apparatus of claim 1, wherein the firstholding unit comprises: multiple first suction portions arranged in afirst direction, among the directions from the central portion of thefirst substrate toward the peripheral portion thereof, in which thebonding region between the first substrate and the second substrate isexpanded fastest; and multiple second suction portions arranged in acircumferential direction with the first suction portions therebetweenand arranged in a second direction, among the directions from thecentral portion of the first substrate toward the peripheral portionthereof, in which the bonding region between the first substrate and thesecond substrate is expanded more slowly than in the first direction,wherein at least one of an attraction force and a timing for releasingthe attraction of the first substrate is set to be different between thefirst suction portions and the second suction portions.
 4. The bondingapparatus of claim 3, wherein each of the first substrate and the secondsubstrate is a single crystal silicon wafer in which a crystal directionof a surface thereof is [100], and when a direction oriented toward a[0-11] crystal direction parallel to the surface of the first substratefrom the central portion of the first substrate is defined as 0°, themultiple first suction portions are arranged at an interval of 90° withrespect to a direction of 45°, and the multiple second suction portionsare arranged at an interval of 90° with respect to a direction of 0°. 5.The bonding apparatus of claim 3, wherein the first holding unitcomprises: multiple third suction portions arranged at an inner sidethan the multiple first suction portions in the first direction; andmultiple fourth suction portions arranged at an inner side than themultiple second suction portions in the second direction.
 6. The bondingapparatus of claim 5, wherein the first holding unit comprises: a fifthsuction portion which has a circular ring shape and is arranged at aninner side than the multiple third suction portions and the multiplefourth suction portions.
 7. A bonding apparatus, comprising: a firstholding unit configured to attract and hold a first substrate fromabove; a second holding unit provided under the first holding unit andconfigured to attract and hold a second substrate from below; and astriker configured to press a central portion of the first substratefrom above and bring the first substrate into contact with the secondsubstrate, wherein a bonding region between the first substrate and thesecond substrate is classified into a first bonding region and a secondbonding region expanded slower than the first bonding region, and thefirst holding unit is configured to attract and hold a first region of aperipheral portion of the first substrate corresponding to the firstbonding region, and not to attract and hold a second region of aperipheral portion of the first substrate corresponding to the secondbonding region.
 8. A bonding system, comprising: a surface modifyingapparatus configured to modify surfaces of a first substrate and asecond substrate; a surface hydrophilizing apparatus configured tohydrophilize the modified surfaces of the first substrate and the secondsubstrate; and a bonding apparatus configured to bond the firstsubstrate and the second substrate, which are hydrophilized, by anintermolecular force, wherein the bonding apparatus comprises: a firstholding unit configured to attract and hold the first substrate fromabove; a second holding unit provided under the first holding unit andconfigured to attract and hold the second substrate from below; and astriker configured to press a central portion of the first substratefrom above and bring the first substrate into contact with the secondsubstrate, wherein the first holding unit is configured to attract andhold a partial region of a peripheral portion of the first substrate,when a bonding region between the first substrate and the secondsubstrate has vertices of a shape closer to a polygonal shape that isexpanded from a circular shape, the partial region includes a regionintersecting with at least one direction from the central portion of thefirst substrate toward the vertices.
 9. The bonding system of claim 8,wherein the direction from the central portion toward the vertices is adirection in which the bonding region between the first substrate andthe second substrate is expanded fastest.